In several episodes of SG1, Atlantis, and once in SGU a person is able to hold a gate open by sticking just their arm through. The show explains why the gate stays open (to prevent a person from being cutoff), but if matter can only travel one way through a gate how can the person pull their arm back through?

Also how would a gate know that the person is completely through, and not just their arm?

1 Answer 1


People moving through the Stargate are stored in an energy buffer as they enter into it; the matter is transformed into energy and vice versa "on the fly" as it enters and exits the gate. Only when the object (or person) completely passes through the event horizon is the stream sent through to the distant gate.

It does raise some interesting questions, such as how the gate "simulates" someone's bloodflow and such (never mind their neural activity while their brain is partially-encoded!).

The gate has safety protocols in place to prevent it from being shut off under normal circumstances if there is something partially within the event horizon. There are a few instances of things being severed due to a gate being closed prematurely, such as when Teal'C holds the Goa'uld-infested Major Kawalsky's head in the gate in an early episode in order to partially decapitate him.

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    @Joe: There are enough bonds in a complete object that it could simply look for the pull. I mean, if it couldn't somehow figure an object was complete, then how could it possibly put it back together right when if left the other side? Commented Apr 26, 2011 at 4:40
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    Additionally, the event horizon has some level of "intelligence", for lack of a better term; it can discern between a solid object being pushed against it vs. the atmosphere, and in one episode there was even a submerged stargate, demonstrating that the stargate can tell the difference between liquids and solids. It's sufficient to say that an object which is no longer intersecting the plane of the event horizon is completely within the energy buffer.
    – Asmor
    Commented Apr 26, 2011 at 4:50
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    @Asmor: If I recall, the 'water' on that planet had some form of intelligence and was capable of some motion, including shaping itself. The question as to whether the gate held back the water or if the water pulled back from the gate wasn't clearly answered, to my knowledge.
    – Jeff
    Commented Apr 26, 2011 at 12:50
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    @Jeff; Gates can happily open into space without depressurising the entire room they're in, so there's clearly some restrictions there.
    – Phoshi
    Commented Apr 26, 2011 at 13:07
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    I really think there should have been an episode where the gate malfunctions after dialling a water planet and sgc flooding
    – Jonathan.
    Commented Apr 26, 2011 at 14:37

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